Authors
Sara Cohen
Publication date
2006/6/26
Book
Proceedings of the twenty-fifth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Pages
70-79
Description
The query equivalence problem has been studied extensively for set-semantics and, more recently, for bag-set semantics. However, SQL queries often combine set and bag-set semantics. For example, an SQL query that returns a multiset of elements may call a subquery or view that returns a set of elements. As another example, in SQL one can compute a multiset-union of queries, each of which returns a set of answers. This paper presents combined semantics, which formally models query evaluation combining set and bag-set semantics. The equivalence problem for queries evaluated under combined semantics is studied. A sufficient condition for equivalence is presented. For several important common classes of queries necessary and sufficient conditions for equivalence are presented.
Total citations
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Scholar articles
S Cohen - Proceedings of the twenty-fifth ACM SIGMOD-SIGACT …, 2006